1. Field of the Invention
The present invention relates to an air-fuel ratio controller for engines installed in vehicles.
2. Detailed Description of the Prior Art
A conventional air-fuel ratio controller controls quantity of fuel to be injected, using a pressure sensor to detect the pressure level of an intake manifold area downstream from a throttle valve, or a throttle valve opening level sensor for acquiring information about the opening level thereof.
As a concrete procedure, the conventional air-fuel ratio controller controls a quantity of fuel to be injected from an injector having an electromagnetic type fuel injecting valve, by using the width of a pulse being impressed to it by the indirect calculation of the above-mentioned pressure level of the intake manifold or the information about the throttle valve open level.
Also, such a conventional air-fuel ratio controller is provided with a systematic learning function for correcting an error in the value detected by the pressure sensor or the throttle valve opening level sensor, or a valve clearance error, considering a change in the value of air supplied to the engine in accordance with a valve clearance of the engine, and even in the open-loop mode in which the air-fuel ratio feed-back control is not performed, the basic fuel quantity is corrected to a controlled injecting quantity by the value calculated by this learning function so as to improve the precision in an air-fuel ratio.
In the above conventional controller, since the valve clearance of the engine changes its state according to the variation of the temperature thereof, if the learning function starts immediately after the engine starts, the error in the valve clearance becomes great as the temperature of the engine is not stabilized yet.
Thus, if the fuel quantity to be injected in the open loop mode, which is predetermined based on the temperature-stabilized state of the engine, is corrected by the pulse width representing a fuel injecting quantity which is calculated while the temperature of the engine is not stabilized yet (such as the moment immediately after the engine starts), then the air-fuel ratio will be abnormal, and an air quality of the exhaust gas or drivability becomes inferior.